The invention relates to a battery, in particular a lead-acid rechargeable battery, having at least one battery cell connecting element, which has a connector), which has at least one side surface, for connection to at least one plate on a lower face of the connector and a welding lug, which is electrically conductively connected to the connector and has a recess which is bounded by a boundary. According to a second aspect, the invention relates to a method for the production of a battery, in particular of a lead-acid rechargeable battery.
By way of example, batteries in the form of lead-acid rechargeable batteries are used as a starter battery in a motor vehicle. A battery such as this comprises a plurality of electrochemical cells which are connected in series and are separated from one another by an electrically insulating separating wall. Each of the electrochemical cells comprises a positive and a negative plate set, each of which is formed from a plurality of plates. The battery cell connecting element connects the plates of a plate set to one another electrically and mechanically and is also used for the plate set of one electrochemical cell to make electrical contact via a further battery cell connecting element with another plate set of another electrochemical cell, through the separating wall.
In order to allow such an electrical contact, during manufacture of the battery, the battery connecting elements are aligned relative to one another and relative to a recess in the separating wall. Material of the battery cell connecting element is then fused in the vicinity of the recess using hot tongs, in such way that a part of the fused material flows through the recess in the separating wall and makes an electrical contact between the two battery cell connecting elements. This results in a recess or depression, which is bounded by a boundary, being created in the battery cell connecting element.
In the case of lead-acid rechargeable batteries, the connector is generally composed of lead. The tongs have welding platelets at the points where they come into contact with the battery cell connecting elements. The welding platelets are either round or oval, like the recess, since this allows two battery cell connecting elements to be connected through the separating wall by a reliable process.
Batteries such as these generally have only voltages between 6 V and 48 V. However, high power levels of up to several kilowatts are required in modern motor vehicles, as a result of which heavy currents flow through the battery cell connecting elements when on load. Currents such as these result in undesirable heating, because of the internal resistance of the battery, and this is disadvantageous. Furthermore, the internal resistance of the battery disadvantageously limits the maximum power which can be emitted from the battery.
The invention is based on the object of overcoming disadvantages in the prior art.
The invention solves the problem by a battery of this generic type in which, on a section which is adjacent to the side surface of the connector, the boundary of the recess of the battery cell connecting element has a profile which corresponds to a contour of the side surface of the connector. In particular, the boundary has a profile which corresponds to the contour of the side surface at a point which is adjacent to the section.
According to a second aspect, the invention solves the problem by a method having the features of claim 16.
A battery cell connecting element such as this advantageously means that an electric current which flows from one plate through the connector and the welding lug through the separating wall to a further battery cell connecting element is subject to a resistance within the welding lug which is essentially independent of the current path. This results in an area-related current density which is essentially the same over that part of the boundary which corresponds to the contour of the upper face of the connector. The material which is available for electrical conduction of the current in the welding lug is therefore optimally used for the current flow, thus making it possible to achieve a reduced internal resistance. This reduces the undesirable heating of the battery during operation, and allows the battery to emit more power.
If a maximum acceptable internal resistance is specified, then the invention alternatively makes it possible to save material of which the welding lug is composed, for example lead.
A further advantage is that the invention allows the battery cell connecting elements to be connected by a reliable process.
For the purposes of the present description, the expression a side surface means in particular any surface which bounds the connector. Furthermore, the expression a contour means in particular the macroscopic geometric form of the surface of the side surface. There is no need for the contour to have a structure. A macroscopically flat upper face also has a contour, specifically a flat surface or plane. Furthermore, there is no need for the boundary to correspond to the contour of the side surface everywhere where it runs adjacent to the side surface of the connector. In particular, it is possible for the boundary to correspond to the upper face of the connector at a plurality of sections of the contours which are separate from one another and are adjacent to the upper face of the connector.
In one preferred embodiment, the boundary has a linear profile in places. This is particularly advantageous in the situation in which the contour of the side surface of the connector likewise has areas with a linear profile in places. The recess particularly preferably has an essentially polygonal plan area, in particular an essentially triangular plan area.
In one particularly preferred embodiment, the boundary runs essentially equidistantly from the contour of the side surface in a section which is adjacent to the side surface of the connector. By way of example, this is achieved in that, when the recess has an essentially polygonal plan area, one side of the polygon is aligned with respect to the adjacent side surface of the connector. In particular, one side of the polygon can be aligned with respect to an upper face or to a side surface of the connector, and in particular can run parallel to it.
If the welding lug has a constant thickness, then this results in the electrical resistance being independent of the current conduction path. The expression that the boundary runs “essentially” equidistantly from the contour of the side surface means that there is no need for it to be strictly mathematically equidistant. In particular, it is sufficient for the boundary to deviate from strict mathematical equidistance to such an extent that the internal resistance is less than 5% above the value which would be achieved with strict mathematical equidistance.
Particularly preferably, the boundary runs essentially equidistantly from the contour of the upper face in all the sections which are adjacent to the upper face of the connector. This has the advantage that it makes it possible to achieve a particularly low battery internal resistance by means of a battery cell connecting element such as this.
In one preferred method, the connection is a weld, with a boundary pointing downward on a section which is adjacent to the side surface of the connector, during the welding process. This has the advantage that cavities cannot be formed, or can be formed only at points with little disturbing effect. This is because any enclosed air bubbles rise upward during the welding process and therefore gather at a point which is at the maximum distance from the section which is adjacent to the side surface and where there is only a low current density during operation of the battery.
A method is particularly preferable in which the boundary additionally has two sections which are adjacent to one another, have a linear profile, form a corner with one another and, when the two battery cell connecting elements are connected, the corner represents the highest point of the recess. This corner preferably faces away from the side surface of the connector. In this case, any rising air bubbles are concentrated in the corner, combine to form larger air bubbles, and escape particularly quickly. This therefore results in a particularly low cavity density.